(a) Field of the Invention
The present invention relates to a method of boning the dark meat of a chicken by a belt-shaped cutter and to an apparatus for implementing the method.
(b) Description of the Prior Art
These days, the breeding and slaughting, and handling and processing as well, of edible fowl have been rapidly increasing in scale along the continual expansion of convenience food market. In this field of industry, many different processings have been automated and are under automation; however, the separation of meat from the bone of raw thigh meat, namely, boning of poultry leg is yet done manually. The reason why the boning of poultry leg by machine or automated boning has not yet been successfully established lies in the fact that such meats are different in shape from one to another. Namely, this difference makes it difficult to separate the meat from the bone without visual checking and manual cutting. The automation of this boning process needs many feedback sensors and a large-scale computer; however, such a system is very expensive and does not economically pay.
Recently, however, a method of boning the poultry leg using a belt-shaped cutter has been developed. By applying this method in practice, a capability of automatically boning poultry leg has been provided.
This boning technique will be outlined in the following, referring to FIG. 1.
The belt-shaped cutter 1 is wound nearly perpendicularly on the bone 2a of a poultry leg 3, and it is moved circumferentially (in the direction of arrow R) along the surface of the bone 2a. In this example, the belt-shaped cutter 1 is reciprocally driven mainly in the directions of arrows F and G. As moved in this way, the belt-shaped cutter 1 will work to separate the meat from the bone not by drawing the bone, but by making a cut between the bone and meat. Consequently, by sliding the belt-shaped cutter on the bone axially thereof as indicated with the arrow B and a slower speed than in the above-mentioned circumferential direction, it is possible to separate the bone 2a and meat 3a from each other with a relatively small force.
Since it has a width W, when it comes near to the joint 4, the belt-shaped cutter 1 can successfully separate the meat 3a from the bones 2a and 2b along the envelope defined by the bone ends as shown with the arrow D with the ligaments 5 remained attached to the bones 2a and 2b and without cutting in, or falling in between, these bones 2a and 2b.
However, there are several problems to be solved in adopting this method for boning of the poultry leg.
One of the problems is the difficulty in keeping the two bones, namely, thigh bone and tibia, in the poultry leg arranged in a straight line. The explanation will be made with reference to FIG. 2. In case of the poultry leg, the tibia 2a ' corresponds to said bone 2a, the thigh bone 2b' to said bone 2b, and the knee joint 4' to said joint 4. When it is tried to put the thigh bone 2b' and tibia 2a' in a straight line, a limit will be encountered in the bending angle of the knee joint 4'. The angle .theta. shown will be not less than 15.degree. unless such a large force as would destroy the joint tissue is applied to the knee joint.
With an apparatus 6 so constructed that a belt-shaped cutter 1 is held at both ends thereof and driven reciprocally as indicated by the arrows G and F, smooth boning of any poultry leg could not be done unless the belt 1 can be moved along the tibia 2a' and then the thigh bone 2b' while being kept perpendicular to the bones 2a' and 2b' with the belt tension kept constant.
Another problem is found in the fact that the bones in poultry leg are thick at their portions near the knee joint 4'. In case many poultry legs are boned in succession, it is difficult to pass the portion wound on the bone of the belt-shaped cutter 1 along the profile of the bones in all the polutry legs since the polutry legs have the knee joints 4' different in thickness from one leg to another.
For working out a practically automatic boning machine adopting the above-mentioned method, it is essential that the belt-shaped cutter 1 can be easily and efficiently wound on the bone 2a in the preliminary step of the boning procedure, and also that the belt-shaped cutter can be easily and efficiently removed from the bone after the separation of the meat from the bone. Otherwise, the efficiency of subsequent meat processing will be low.
For winding on the bone and circumferential moving of the belt-shaped cutter 1, the cutter must be made of a thin elastic material such as spring steel, stainless steel, synthetic resin, etc. If it is not, the cutter could not be smoothly moved on the bone. When the belt-shaped cutter 1 wound on the bone 2a is reciprocally driven by a drive unit 6 in the directions of arrows G and F while the drive unit 6 is moved over a distance L.sub.1 rightward as indicated with an arrrow H with both ends of the belt-shaped cutter 1 connected to the drive unit 6, the portion wound on the bone 2a of the belt-shaped cutter 1 also slides rightward, but the belt edge having been longitudinally straight is deflected like bow, resulting in a move of the wound portion of the belt over a distance L.sub.2, because the belt-shaped cutter 1 is made of a thin elastic material. The distance L.sub.2 is smaller than that L.sub.1. Thus, the portion wound on the bone 2a of the belt-shaped cutter 1 cannot precisely follow up with the movement of the drive unit, with the reduction in efficiency of boning. The lateral edge 1a of the belt-shaped cutter 1 may not be provided with any too sharp blade. The reason is that if a sharp blade is provided on the lateral edge 1a of the belt-shaped cutter 1, when the belt-shaped cutter 1 wound on the bone 2a is slid reciprocally in the direction of arrow B, the belt will not slide on the ligaments 5 as indicated with the arrow B but it will cut into the ligaments 5 and bones 2a, performing no stable boning function. However, if the blade on the lateral edge 2a of the belt-shaped cutter 1 is too dull, the efficiency of boning decreases.
The blade provided on the lateral edge 1a of the belt-shaped cutter 1 should be neither too sharp nor too dull.